This application is a United States national phase application of pending German Application Serial No. 100.16 793.4, filed Apr. 5, 2000, and herein claims priority of to the afore-referenced pending application.
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1. Field of the Invention
This invention relates to a device for feeding sheets of a recording medium from a stack to an office machine according to the definition of the species of claim 1.
In the case of office machines which process individual sheets of a recording medium, in particular paper sheets, it is necessary to feed the sheets which are kept in a stack individually to the office machine.
To do so, it is known that separating rollers can be made to act in a frictionally engaged manner on the top sheet of the stack, pushing the top sheet against separation comers so that the top sheet springs over the separation corners and is separated from the following second sheet of the stack. This single feed by means of separation corners depends greatly on the properties of the sheet, in particular the stiffniess of the sheet. Therefore, this device is suitable only for a relatively narrow range of sheet qualities.
The sheet quality, i.e., its stiffness, the paper weight, etc., are less influential in separation and single feed of sheets where pressure is applied over the top sheet of the stack to cause the sheet to form a wave (wave generator), thereby releasing it from the following second sheet of the stack. The top sheet released from the second sheet in this way is at the same time advanced forward away from the stack and sent to the office machine.
2. Related Art
A device of the generic type defined in the preamble based on this principle is known from German Patent 178,765. With this device, shingling parts made of steel are mounted on a continuously rotating chain and are guided over the top sheet of the stack under pressure and supported by a guide skid. Such shingling parts guided over a sheet under pressure may cause pressure marks and traces on the surface of the sheet. This is a disadvantage especially when working with grades of paper having a sensitive surface, e.g., supercalendered paper. In addition, it is known that rollers which are mounted so they can rotate may be passed over the top sheet as shingling elements. To do so, the rollers are mounted on the periphery of a rotationally driven disk. According to German Patent 205,058, the disk rotates about an axis parallel to the plane of the sheet and perpendicular to the direction of feed. According to German Patent 164,228, the disk is arranged in the same way, and the rollers mounted on its periphery are also spring-mounted radially. According to U.S. Pat. No. 4,165,870, the disk can rotate about an axis perpendicular to the plane of the sheet and the direction of feed, whereby the rollers running in the direction of feed can be brought in contact with the top sheet of the stack by tilting the axis. The use of rotationally mounted rollers as shingling elements reduces the problem of pressure marks and traces, but it cannot completely eliminate it in the case of sensitive paper surfaces. Because of the arrangement of rollers on the periphery of a disk, the rollers engage with the top sheet of the stack only over a very short distance in the direction of feed. Therefore, to generate a flexing effect sufficient to loosen the top sheet, a relatively high pressure of the rollers on the sheet is necessary, but this in turn results in more pressure marks.
A device of is disclosed which may enable a wide range of sheet qualities to be separated for single feed and fed to the machine reliably, while preventing most pressure marks on a surface of the sheets.